i BYZANTINE ARCHITECTURE /V'' • "fa" ? § ?... the case of these two memorial chapels, their rfafrow3 long-? stretched plan is evidently due to the desire t\%eep theif' eastern apses in line with the east end of this churches they adjoin, and at the same time to bring the western end to the narthex from which they were entered. They are covered with two domes, a system perhaps derived from S. Irene (p. 94). Kefel6 Mesjedi (p. 257), which at first sight resembles a single hall church roofed, in wood, was a refectory. Its plan may be compared with that of the refectory at the monastery of S. Luke at Stiris.1 II. ARCHITECTURAL FEATURES AND DETAILS Apses.—A fully developed Byzantine church terminated in three apses : a large apse, with the bema or presbytery, in the centre ; on the right, the apse of the prothesis where the sacrament was prepared ; on the left, the apse of the diaconicon, where the sacred vessels were kept. Although there is proof that the prothesis and the diaconicon were in use at a very early period, yet many churches of the great period, as for example S. John of the Studion, SS. Sergius and Bacchus, and S- Sophia, dispensed with these chambers as distinct parts of the building. They were also omitted in small churches of a late date, where they were replaced by niches on either side of the bema. The three apses usually project from the east wall of the church, but occasionally (p. 248) the two lateral apses are sunk in the wall, and only the central apse shows on the exterior. As a rule the apses are circular within and polygonal without. It is rare to find them circular on both the interior and the exterior (p. 203), and in Greece such a feature is generally an indication of late date. An octagonal plan, in which three sides of the octagon appear3 sometimes with short returns to the wall, is the most common ; but in later churches polygons of more sides are used, especially for the central apse, and these are often very irregularly set out. Some of the churches of Constantinople show five, and even seven sides. 1 Schultz and Barnsley, The Monastery ofS. Luke at Stiris, p. 13, fig. 6.